Lithography exposure apparatuses are commonly used to transfer images from a reticle onto a semiconductor wafer during semiconductor processing. A typical exposure apparatus includes an illumination source, a reticle stage assembly that positions a reticle, an optical assembly, a wafer stage assembly that positions a semiconductor wafer, and a measurement system that precisely monitors the position of the reticle and the wafer.
The illumination source generates a beam of light energy that is directed at the reticle. The projection optical assembly directs and/or focuses the light from the reticle to the wafer. The reticle stage assembly includes a reticle stage and one or more motors to precisely position the reticle relative to the projection optical assembly. Similarly, the wafer stage assembly includes a wafer stage and one or more motors that precisely position the wafer relative to the projection optical assembly.
Depending upon the wavelength of the light energy generated by the illumination source, the type of fluid between the illumination source and the wafer can greatly influence the performance of the exposure apparatus. For example, some types of light energy are absorbed by oxygen and other gases. Absorption of the light energy can lead to losses of intensity and uniformity of the light energy. Accordingly, the performance of the exposure apparatus and the quality of the integrated circuits formed on the wafer can be enhanced by controlling the environment around one or both stages.
One way to control the environment around a stage includes positioning a chamber around the stage. Subsequently, the desired environment can be created within the chamber around the stage. One type of controlled environment is a vacuum.
Unfortunately, stages generate heat from on-board actuators or sensors, as well as from absorption of the exposure radiation on the reticle or wafer. This heat must be removed in order for the stages to perform correctly. Traditional means include convection, conduction and radiation heat transfer to the surrounding air and surfaces for stages operating in air, in addition to heat transfer through coolants circulated through the stages and hoses to a fixed heat exchanger. However, in a vacuum, convection and conduction through air is absent; only radiant cooling remains, which is typically inadequate. Pumping coolant through hoses is much more difficult because the hoses must be vacuum compatible in addition to their other required properties. In either case, the hoses are displaced during stage motion, and this motion in turn perturbs the stage motion, making precision motion difficult.